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The origins of the Acheulean in East Africa

Final Report Summary - ORACEAF (The origins of the Acheulean in East Africa)

The emergence of the Acheulean is presently one of the most debated topics in the African Early Stone Age, with high-profile papers pushing back in time the origins of this technology and associated hominins. In this context, Olduvai Gorge should play a pivotal role, since it is one of the few sites containing a continuous stratigraphic sequence from the Oldowan through the early Acheulean, thus allowing researchers to investigate the environmental, biological and cultural contexts of this technological change. In this context, ORACEAF has conducted large scale excavations at Olduvai between 2012-2016, targeting primarily the stratigraphic interval of Middle Bed II, where the latest Oldowan and the earliest Acheulean assemblages are documented. Fieldwork was driven by a number of research questions, including; what are the technological characteristics of the late Oldowan hominins in Olduvai? Are there differences in the food procurement strategies of late Oldowan and early Acheulean hominins? What are the differences in the ecological adaptations and land-use behaviours of late Oldowan and early Acheulean hominins? When, exactly, did the Acheulean first appear at Olduvai, and how does this compare to other early Acheulean sites in Africa?

Our geological work has provided a refined context for Middle Bed II, including a higher resolution stratigraphic framework, radiometric dating and insights into site formation processes and environments. Paleoecological studies, which have included analysis of diatoms, carbon and oxygen stable isotopes and tooth use wear, among others, have contributed to study changes in the vegetation and faunal communities occurred at this time, and their impact in adaptations of the latest H. habilis populations at Olduvai Gorge. Extensive archaeological excavations in late Oldowan and early Acheulean sites have produced detailed trench stratigraphic correlations, landscape reconstructions and a systematic study of site formation processes based on spatial analysis, taphonomic signatures and sedimentological features, which enable to better understand biotic and abiotic dynamics in the accumulation of the rich Olduvai assemblages. Zooarchaeological analysis of late Oldowan bone assemblages have revealed that the majority of carcasses were obtained by hominins through scavenging from large carnivore kills. Geochemical and petrographic analysis of archaeological stone tools from several Middle and Upper Bed II sites has enabled us to produce a comprehensive dataset and characterization of the metamorphic, igneous and sedimentary rocks used by Olduvai hominins. Technological studies characterize late Oldowan sites as core-and-flake assemblages where simple flaking techniques are accompanied by an increase of retouched flake frequencies and battered tools, when compared to Olduvai Bed I and Lower Bed II. Handaxe assemblages show neat differences with the earlier Oldowan and suggest a clear technological rupture with the previous period.

In addition to results of field and laboratory work, ORACEAF has produced relevant methodological innovations with an application to Early Stone Age research worldwide. We have pioneered an integrated approach to macroscopic, microscopic and spatial analyses of experimental and archaeological stone tools, thus contributing to create a referential framework in which Early Stone Age lithics can be interpreted. Our use of Unmanned Aerial Vehicles and photogrammetric techniques have provided detailed digital cartographic basis for geological and paleoanthropological research, as well as new monitoring tools for the conservation of cultural heritage. Our cross-disciplinary approach to stone tool analysis has fostered collaborations with primatology, geochemistry and GIS research, among others, and contributed importantly to reconsider theories of the emergence and evolution of human technology.